1. Field of the Invention
The present invention relates to a tray carried in and out of a heat treatment furnace together with a workpiece placed on the tray, and a heat treatment method using the tray.
2. Description of the Related Art
Heat treatment is a generic term of treatment in which properties of a workpiece are changed by heating or cooling. The heat treatment includes quenching, tempering, annealing, normalizing, oil quenching, blackening treatment, etc. (see JP-A-2003-113421 as Patent Literature 1). In a manufacturing step of a laminated iron core such as an armature iron core of an electric motor or a generator, various items of heat treatment are conducted. For example, the oil quenching, the annealing, the blackening treatment, etc. are conducted. The oil quenching is treatment in which the oil content such as stamping oil adhering to a surface of a prime plate is evaporated and removed in a processing step. The annealing is also called drawing back, and is treatment in which an internal stress or a strain of the prime plate is removed (see JP-A-11-332183 as Patent Literature 2). The blackening treatment is also called bluing, and is treatment in which a coating (so-called black rust) of triiron tetroxide (Fe3O4) is produced on the surface of the prime plate for rust prevention. The oil quenching, the annealing and the blackening treatment may also be conducted continuously. For example, FIG. 1 of JP-B-7-42508 as Patent Literature 3 discloses a continuous annealing and bluing apparatus in which a deoiling furnace 2, an annealing furnace 3 and a bluing furnace 4 are connected by a conveyance path 1 and a workpiece is carried in and out of each of the furnaces.
JP-A-2003-113421 mentions that many workpieces are placed on a conveyance jig and are carried in a heat treatment furnace and are heat-treated and then are out of the heat treatment furnace and are conveyed to the next step. The conveyance jig is also called a tray or a pallet, and is generally constructed in a grid shape so that the workpieces are equally heated and cooled (see JP-A-2003-113421 as Patent Literatures 1, JP-A-2008-38194 as Patent Literature 4, and JP-A-2009-249649 as Patent Literature 5).    Patent Literature 1: JP-A-2003-113421    Patent Literature 2: JP-A-11-332183    Patent Literature 3: JP-B-7-42508    Patent Literature 4: JP-A-2008-38194    Patent Literature 5: JP-A-2009-249649